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LECTURE LIII. 



ON ELECTRICITY IN EQUILIBRIUM. 



JL HE phenomena of electricity are as amusing and popular in their external form 

 as they are intricate and abstruse in their intimate nature. In.examiiiing these 

 phenomena, a philosophical observer will not be content with such exhibitions as 

 dazzle the eye for a moment, without leaving any impression that can be instruct- 

 ive to the mind, but he will be anxious to trace the connexion of the facts with 

 their general causes, and to compare them with the theories which have been 

 proposed concerning them : and although the doctrine of electricity is in 

 many respects yet in its infancy, we shall find that some hypotheses may be 

 assumed, which are capable of explaining the principal circumstances in a 

 simple and satisfactory manner, and which are extremely useful in connect- 

 ing a multitude of detached facts into an intelligible system. These hypo- 

 theses, founded on the discoveries of Franklin, have been gradually formed 

 into a theory, by the investigations of Aepinus and Mr. Cavendish, combined 

 with the experiments and inferences of Lord Stanhope, Coulomb, and 

 Robison. 



We shall first consider the fundamental hypotheses on, which this 

 system depends, and secondly the conditions of equilibrium of the 

 substances concerned in it; determining the mode of distribution 

 of the electric fluid, and the forces or pressures derived from its action 

 when at rest; all which will be found to be deduced from the theory 

 precisely as they are experimentally observable. The motions of the 

 electric fluid will next be noticed, as far as we. can form any general con- 

 clusions respecting them; and the manner in which the equilibrium of elec- 

 tricity is disturbed, or the excitation of electricity, will also be considered ; 

 and, in the last place, it will be necessary to take a view of the mechanism or the 



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